1. Field of the Invention
The present invention generally relates to color image forming apparatuses, and more specifically, to a color image forming apparatus such as a copier, printer, or facsimile, having a function for correcting positional error of a written image.
2. Description of the Related Art
Conventionally, in an image forming apparatus configured to form images in color, a color image is formed by overlapping plural basic color images. Because of this, in order to overlap the basic color images on a recording medium precisely, positions of basic color images should be adjusted. A state where the positions of the basic color images are not adjusted but are shifted is called positional error. Due to generation of the positional error at the basic color images, color shifting is generated at the overlapped image.
In order to prevent the color shift, a mark for detecting the positional error of each of the basic colors is formed at an intermediate transferring medium and a position of the mark is detected so that whether the positional shift is generated is detected.
Techniques whereby the color shifting is prevented by correcting the position of the image of each of the basic colors when the positional error is generated are discussed in, for example, Japanese Laid-Open Patent Application Publication No. 2003-337456 and Japanese Laid-Open Patent Application Publication No. 2005-31263.
More specifically, Japanese Laid-Open Patent Application Publication No. 2003-337456 describes that, for the purpose of stabilization of the color shifting, a proper offset value whereby a color shifting amount with time is made minimum until next color shifting correction control time is added to a correction value so that writing start position or scanning width in a main scanning direction and writing start position in a sub-scanning direction are corrected.
In the technique of Japanese Laid-Open Patent Application Publication No. 2003-337456, while the color shifting is stabilized, it takes time for control for correcting the color shifting and therefore down time may be generated.